High-performance microscale optoelectronic infrared-to-visible upconversion devices and their use as the biomedical light sources

Photon upconversion with the transformation of low-energy photons to high-energy photons is of significant interest for broad applications in biomedicine for stimulation, sensing, and imaging. Conventional upconversion materials rely on non-linear light-matter interactions, exhibit incidence dependent efficiencies and require high power excitation. Here, we present self-powered, micrometer-scale optoelectronic devices for high-performance near-infrared (∼810 nm) to visible (630 nm red or 590 nm yellow) photon upconversion. Thanks to its unique photon-electron conversion process, these thin-film, ultra-miniaturized devices realize fast upconversion that is linearly dependent on incoherent, low-power excitation, with a quantum yield of ∼1.5%. Encapsulated, freestanding devices are transferred onto heterogeneous flexible substrates and show desirable biocompatibilities within biological fluids and tissues. Demonstrations of optogenetic stimulation with upconversion devices as implantable light sources have successfully performed in vitro and in vivo scenarios. This approach provides a versatile route to achieve upconversion throughout the entire visible spectral range at lower power and higher efficiency than has previously been possible.